A power transmitting apparatus of a vehicle, such as an automobile, that transmits engine power to the wheels is required to absorb both radial and axial displacements as well as a moment variation of the power transmitting apparatus from wheels. The moment variation is caused by bounds and cornering of the vehicle during running on a rough road. Accordingly, one end of a drive shaft, interposed between an engine side and a driving wheel side of the power transmitting apparatus, is connected to a differential gear unit, via a slide type constant velocity universal joint. The other end of the drive shaft is connected to a wheel via a wheel bearing apparatus including an immovable type constant velocity universal joint.
Recently, improvements in fuel consumption are strongly desired in view of resource saving or environmental pollution. A reduction of weight of the wheel bearing apparatus, among other automobile parts, is especially desired to achieve improvements in fuel consumption. Although various proposals have been made regarding the weight reduction of the wheel bearing apparatus, in assembling sites and servicing markets of automobiles, reduction of cost by simplifying the assembling and disassembling works has also been a very important factor.
FIG. 5 shows one representative example of a wheel bearing apparatus that can satisfy these requirements. The wheel bearing apparatus is formed as a separable unit with a double row rolling bearing 51 and a constant velocity universal joint 52. The double row rolling bearing 51 includes an outer member 53, inner member 57 and double row balls. The outer member 53 is integrally formed, on its inner circumference, with double row outer raceway surfaces 53a, 53a. The inner member 57 includes a wheel hub 55 and an inner ring 56 formed with a double row inner raceway surfaces 55a, 56a, respectively. The double row balls 58, 58 are rollably contained between the outer and inner raceway surfaces. The double row inner raceway surfaces 55a, 56a of the inner member 57 are arranged opposite to the double row outer raceway surfaces 53a, 53a of the outer member 53. The wheel hub 55 has a wheel mounting flange 54 integrally formed at its one end. A cylindrical portion 55b axially extends from the inner raceway surface 55a. The inner ring 56 is press-fit onto the cylindrical portion 55b of the wheel hub 55. The inner ring 56 is axially rigidly secured by a caulking portion 59. The caulking portion is formed by plastically deforming the cylindrical portion 55b of the wheel hub 55 radially outward. A torque transmitting face-spline 60 is formed on an inner end face of the caulking portion 59.
The constant velocity universal joint 52 includes an outer joint member 61, a joint inner ring 62, a cage 63, and torque transmitting balls 64. The outer joint member 61 includes a cup-shaped portion 65 and a shoulder portion 66 that forms the bottom of the cup-shaped portion 65. An inner thread 66a is formed in the bottom of the cup-shaped portion 65. An end face of the shoulder portion 66 is formed with a face-spline 67. The face-spline 67 engages the face-spline 60 formed on the inner end face of the caulking portion 59. Thus, a rotational torque from a drive shaft (not shown) can be transmitted to the wheel mounting flange 54, via the constant velocity universal joint 52 and the wheel hub 55.
A fastening bolt 68 is screwed into the inner thread 66a on the shoulder portion 66. This fastening engages the face-splines 67, 60 to each other to unite the separate double row rolling bearing 51 and the constant velocity universal joint 52. Accordingly, it is possible to reduce both weight and size of the wheel bearing apparatus and to simplify assembly and disassembly.
As shown in FIG. 6, a caulking tool 69 forms the face-spline 60 of the caulking portion 59 simultaneously with the formation of the caulking portion 59. The caulking tool 69 is formed with a guiding portion 70a with a tapered configuration at its tip end. A mandrel 70 is adapted to be arranged at an inclined angle relative to an axis of the wheel hub 55. An inner sleeve 71 is formed with teeth 71a at its tip end. An outer sleeve 72 has a confining portion 72a to limit radial expansion of the caulking portion 59. A coil spring 73 is interposed between the outer and inner sleeves 72 and 71. Thus, the outer sleeve 72 can be moved independently relative to the inner sleeve 71.
The caulking tool 69 is made to have a swing motion by rotating the wheel hub 55 around its central axis. The end portion of the cylindrical portion 55b of the wheel hub 55 is plastically deformed by the swing motion of the caulking tool 69. Thus, the caulking portion 59 is formed. During the formation of the caulking portion 59, the face-spline 60 is also simultaneously formed by pushing the teeth 71a of the inner sleeve 71 against the caulking portion 59. See, U.S. Pat. No. 4,893,960.
In such a wheel bearing apparatus, since the face-spline 60 can be formed simultaneously with the caulking portion 59 by swing caulking, it is possible to improve the workability as well as to reduce the number of machining steps. Thus, it is possible to reduce the manufacturing cost. However, there have been several problems associated with the manufacturing. One such problem is that metal molds of the caulking tool are complicated and thus their machining, assembly and management manpower are increased. Another problem is that material of the wheel hub is liable to enter into gaps between the mandrel 70 and sleeves 71, 72. Thus, burrs are generated and separate burrs remain in the working site and therefore reduce the workability. Another problem is that burrs generated on the caulking portion 59 and/or the face-spline 60 detracts from the quality of the wheel bearing apparatus.